The invention relates to a material in which alkali metal atoms are taken up between graphitic layers of carbon atoms, on a material that can be prepared from such a graphitic material loaded with alkali metal, e.g. by allowing the graphitic material to react either with compounds with reactive hydroxyl ions or with water or with reducible metal ions. The invention further relates to the use of these graphitic materials as water remover, as basic catalyst, as alkali metal reagent, and as filler for polymers.
It is technically very difficult to prepare and stabilize finely divided alkali metals.
A conventional technique to produce finely divided metals is to start from oxides or other reducible compounds of the desired metals that can be properly brought into a finely divided form. In general, oxides or other ionic compounds are much simpler to bring into a finely divided form than metals. This largely applies to alkali metals which have a low melting point and are readily deformable. Subsequently, the finely divided oxides or other ionic compounds are reduced to the corresponding metals.
In the case of relatively base metals, such as nickel or cobalt, this reduction is preferably carried out by heating the material in a stream of a gaseous reducing agent. The reduction is carried out at a lowest possible temperature to inhibit sintering of the resulting metal particles as much as possible. When using not too high a reduction temperature and/or a short time in which the reduction is carried out, it is possible to obtain powders of metal particles in which the conglomerates of the elementary particles have a low mechanical strength and can be readily processed into smaller particles.
More noble metals, such as platinum, palladium or silver, can already be reduced at much lower temperatures. For this reason small particles of such metals are often prepared by carrying out the reduction in liquid phase. As reducing agent a soluble organic compound is mostly used, e.g. formalin, although the reduction can also be carried out by passing hydrogen through a(n) (aqueous) solution of a suitable soluble compound of the metal ion to be reduced.
The processes described in both preceding paragraphs cannot be used for the very base alkali metals.
When finely divided metals must be used at higher temperatures or must be reduced at higher temperatures, a so-called carrier is mostly used. A carrier is a finely divided material that does not sinter at (highly) elevated temperatures. Known carriers are alumina and silica. The metal compound to be reduced is applied in finely divided form to the surface of this carrier, after which the reduction is carried out at elevated temperature in a stream of gaseous reducing agent. Mostly, the sintering of the metal particles formed can be largely suppressed in this way. An additional advantage is that the carrier can be used as porous bodies having dimensions of, e.g., 0.5 cm. In a technically simple manner, a gas stream can be passed through a packed bed of such carrier bodies loaded with the compound to be reduced.
The reduction with a gaseous reducing agent is not possible with alkali metals applied to a carrier. Not only does the position of the thermodynamic equilibrium not allow reduction, but most of the commercial carrier materials react rapidly with alkali metal ions.
Yet there is a great need for alkali metals in finely divided form. In many reactions, and in particular in many organic chemical reactions, alkali metals are used, of which the relatively small alkali metal surface is a drawback. Also, alkali metals are frequently used as siccative for organic liquids; however, the use of, e.g., sodium filament is technically difficult, certainly on a larger scale. One of the objects of the invention is to provide alkali metals having a large accessible surface.
For thermal dehydrogenation reactions it is attractive to have a material that can react to form stable metal hydrides. It is thus possible to drastically reduce the hydrogen partial pressure, so that at a lower temperature the equilibrium moves in the desired direction. Disintegration of the compound to be dehydrogenated can thus be inhibited. An example is the dehydrogenation of ethyl benzene to styrene, which reaction is now carried out at highly elevated temperature. It is known that alkali metals form hydrides that are still stable at rather high temperatures; these hydrides disintegrate at even higher temperatures. Consequently, such metal hydrides offer the possibility to carry out dehydrogenations at relatively low temperatures.
Another important use of alkali metals in finely divided form is the preparation of finely divided other metals. The alkali metal is then used as reducing agent, as is conventional in the preparation of base metals, such as titanium, in which the reduction is generally carried out with magnesium metal. With specific base metals it is very difficult to carry out the reduction with a gaseous reducing agent. A relatively unexpected example is metallic iron. When the iron is applied to a suitable carrier material, it is difficult to rapidly reduce the water vapor pressure within the porous material to such an extent that reduction to the metallic iron is thermodynamically possible. Consequently, only reduction to divalent iron initially occurs. Divalent iron rapidly dissolves in silica, while it rapidly reacts with alumina to form a spinel; in both cases the iron cannot be reduced any more. Metals that are less noble than iron, such as titanium, cannot be reduced with a gaseous reducing agent at all. With finely divided alkali metals such base metals can also be reduced. Thus, for instance, it is possible to prepare an iron-titanium alloy in finely divided form. Such an alloy is of great interest to the storage of hydrogen. With the finely divided alloy disintegration does not occur, which causes great problems with such an alloy in not finely divided form upon desorption of hydrogen.
There is technically also a great need for finely divided solids of alkaline reaction. First of all, this applies to fillers of polymers. Both in polymers prepared with Ziegler-Natta catalysts and in polyvinyl chloride hydrogen chloride is released. This released hydrogen chloride adversely affects the color and the mechanical properties of the polymer. When processing the polymer, released hydrogen chloride additionally causes damage to the processing apparatus and is therefore highly undesirable. It is of great interest to have finely divided solids of alkaline reaction that can be processed in such polymers, and which can thus react with released hydrogen chloride. According to the prior art hydrotalcites are used for that purpose, which, however, are not very finely divided. occasionally, organometallic compounds of heavy metals, such as lead, are also used, which gives rise to environmental pollution. Of great significance to this use is that the polymer in which the solid compound of alkaline reaction must be processed properly moistens this solid. This is not the case with the hydrophilic hydrotalcites, so that this material must be covered with specific compounds.
A further use of finely divided solids of alkaline reaction is the use as catalyst in basically catalyzed reactions. At the moment a lot of soda and lye is consumed for such reactions, in which the catalyst cannot be recovered. A solid catalyst of alkaline reaction would therefore be very valuable.
A further object of the invention is therefore to provide finely divided alkaline solids.